Application of Mill Treatment to Digested Liquid for Agricultural Utilization

Abstract

Mill treatment was applied to digested liquid taken from a methane fermentation plant in order to miniaturize particle size of suspended solids. The particle size of the digested liquid decreased from 2-590μm to 0.45-105 μm with a 3 hour mill treatment using 1 mm diameter glass beads (RUN-1). An additional 3 hour mill treatment with 0.3 mm diameter zirconium beads (RUN-2) reduced the particle size to 0.19-11μm. Coliform bacteria were not detected in the 1 h treated liquid of RUN-1, although the raw digested liquid contained 3,600 CFU·ml^-1 of coliform bacteria (CFU: colony forming unit). Viscosity of the digested liquid was approximately 11 mPa·s at 15°C and negatively correlated with temperature. RUN-1 and RUN-2 decreased the raw liquid viscosity by approximately 20%. RUN-1 improved the permeability of the liquid into the soil. A significant difference in the measured relative densities existed between the digested and treated liquids after RUN-1 and 2. However, the difference was less than 2% of the digested liquid density.